The triple-folded buckle, for example, has three plates which are pivotally connected with each other. The three plates comprise a lower plate as a base, a middle plate, and a surface cover as a rotating portion.
Japanese Utility Model Laid Open 6-19527 discloses a lock device for the triple-folded buckle. The device has an engaging portion, a pair of push buttons slidably mounted on the underside of a cover so as to be moved in the lateral direction with respect to the longitudinal direction of a band, and a lock pin projected from a lower plate. The buckle is locked by engaging an engaging portion of each push button with the lock pin, and the lock is released by pushing the push button at the same time.
However, there may occur that the push buttons are pushed by a foreign thing so that the buckle is removed. As means for preventing such a trouble, Registered Utility Model 3001890 discloses a double lock device for the triple-folded buckle. The device has a lock cover pivotally mounted on a lower plate. The lock cover is adapted to be engaged with a pin of a spring-loaded pin attached to a surface cover.
Such a device has disadvantages that the number of parts increases due to the spring-loaded pin, which causes the manufacturing cost to increase. There must provide a space necessary for attaching the spring-loaded pin, resulting in enlargement of the buckle and in complication of construction.
An object of the present invention is to provide a lock device resolving the above described problems.